1,721,038 research outputs found
RC frame structures retrofitted by FRP-wrapping: A model for columns under axial loading and cyclic bending
Full text linkIn order to mitigate the seismic risk of existing RC frame structures not designed with seismic criteria, a widespread strengthening strategy is based on increasing strength and ductility of RC columns by means of Fiber Reinforced Polymer wrapping. The existing models for RC cross-sections wrapped by FRP sheets were developed principally considering pure axial loads with uniform confinement pressure. In seismic areas, RC columns are instead usually subjected to axial load and cyclic bending. In the present work, in order to consider the effective loading conditions, an iterative cyclic model for square RC cross-sections wrapped by composite FRP sheets subjected to axial force and cyclic bending is proposed. The model considers the strain gradient-effect over the cross-section due to the bending loads that change significantly the confinement level of RC cross-section. Moreover, the model has been validated by comparing the numerical outcomes with various cyclic experimental results. The model has been also implemented in an open-source software with distributed plasticity finite elements in order to perform pushover analyses of an existing RC frame structure with different retrofitting strategies to improve the ductility of the columns for lateral forces
A new single-shear set-up for stable debonding of FRP-concrete joints
No full textA new experimental set-up to perform single-lap shear debonding tests on fiber reinforced polymer (FRP) reinforcements bonded to concrete is presented. Back sides of both FRP reinforcement (sheet or plate) and concrete specimen are fixed to an external restraining system and the force is applied to the other side of FRP reinforcement. Hence, a stable debonding process can be experimentally followed, corresponding to the transition between two limit states of perfect bonding and fully debonded reinforcement. Both strain gauges along the FRP reinforcement and LVDT transducers have been used. Tests have been performed on both plates and sheets bonded to concrete specimens with different surface preparations before adhesive application. Shear stress-slips data have been computed from the experimental FRP strain measures. The parameters of a non-linear interface law have been then calibrated and compared with analogous results from experimental data obtained with a conventional set-up. A numerical bond-slip model has been finally used to simulate the experimental tests, adopting the above-mentioned law for the FRP-concrete interface. Numerical results in good agreement with experimental results have been obtained. © 2008 Elsevier Ltd. All rights reserved
Inverse analysis for the calibration of FRP - Concrete interface law
No full textInverse analysis technique is used to derive a non linear mode II interface law for Fiber Reinforced Polymer (FRP) – concrete bonding starting from experimental data. The proposed interface law is based on a fractional formula and includes non linear compliance contributions of adhesive and concrete cover at high shear stresses. It depends on three parameters (maximum shear stress, corresponding slip and an exponent), which are calibrated from experimental results on delamination tests. Values of maximum loads and strains profiles along FRP plates for different bonding lengths are used. Parameter identification is performed by inverse analysis using a Direct Search algorithm. Considerations on well-posedness of the inverse problem adopting different cost functions to minimize the error between experimental and numerical data are given. After parameter identification, numerical results obtained with the proposed interface law are found to be in very good agreement with experimental results
Calibration of a mode II FRP-Concrete interface law by inverse analysis
No full textInverse analysis technique is used to derive a non linear mode II interface law for Fiber Reinforced Polymer (FRP) – concrete bonding starting from experimental data. The proposed interface law is based on a fractional formula and includes non linear compliance contributions of adhesive and concrete cover at high shear stresses. It depends on three parameters (maximum shear stress, corresponding slip and an exponent), which are calibrated from experimental results on delamination tests. Values of maximum loads for different bonding lengths and strains profiles along FRP plates are used. Parameter identification is performed by inverse analysis using a Direct Search technique. Considerations on well-posedness of inverse problem adopting different cost functions are given. After parameter identification, numerical results obtained with the proposed interface law are found to be in very good agreement with experimental results
Corrosion effects on the flexural performance of prestressed reinforced concrete beams
No full textAn experimental campaign aimed at understanding the behavior of corroded prestressed beams is carried out to investigate the effects of low corrosion levels spreading along the entire beams. The results show that corrosion affects the flexural stiffness, the beams’ crack pattern, and the failure conditions. Analytical models, implemented to simulate the experimental investigation, allowed a better interpretation of the obtained results, showing that the flexural performance of the corroded beam is governed by both a prestress loss and a reduction of the strand’s mechanical properties, such as ultimate strength and strain
Assessment of a bond strength model for FRP reinforcement externally bonded over masonry blocks
No full textAccording to recent design Codes and Recommendations, verification against debonding is imperative in the design of strengthening interventions with Fiber Reinforced Polymers (FRP). In FRP – reinforced masonry elements, debonding at reinforcement extremities (end debonding) must be avoided by limiting the maximum force achievable by the strengthening system. This paper proposes design criteria against debonding in masonry elements externally strengthened by FRP sheets. Results of more than 250 bond tests, reported in the literature and carried out over different masonry supports, clay bricks and natural stones, are collected and examined. Formulas for fracture energy of interface bond law and debonding load are assessed starting from the experimental database. In order to provide design formulas according to the Partial Safety Factor Method for Ultimate Limit State verification, mean and characteristic values of the debonding load are determined through statistical methods
Corrosion level estimation by means of the surface crack width
No full textSince the concrete cover cracking is the earliest visible manifestation of corrosion, a relationship between crack opening and corrosion level can be a useful non-destructive tool to estimate the degradation level of an existing RC member. In the present paper, the predictive formulations available in the scientific literature estimating the crack width due to a given corrosion level are accurately described and their reliability is evaluated by a statistical analysis of the error in the predictions. At this aim, an extensive dataset on crack openings of artificially corroded RC specimen reinforced with a single bar, or more bars with large spacing, has been collected. Finally, a novel relationship for the assessment of the corrosion degradation from the surface cracking is presented and validated
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